QoS Management of real-time applications in NVRAM-Based multi-core smartphones

This paper presents a QoS management scheme for real-time applications in multi-core smartphones. Specifically, the proposed scheme guarantees the end-to-end QoS of real-time applications like a movie player, while also provides reasonable latency for other applications. To this end, we analyze the program execution path of smartphones and observe two sources of unpredictable latency that may threaten the deadline-guarantee of real-time tasks. The first is the sporadic execution of garbage collection performed in NAND flash memory and the second is the time-quantum-based completely fair scheduler used in Android. Our scheme handles these situations by two architectural supports with novel mechanisms. First, we adopt high performance NVRAM as the storage of real-time applications. By storing real-time applications and their data in NVRAM, constant I/O latency is guaranteed as NVRAM does not incur garbage collection. Second, we propose a dual-purpose scheduler, in which one core is exclusively used for a real-time task. Though CPU cycles may be wasted during the I/O execution, we show that the CPU utilization is not degraded largely as NVRAM provides sufficiently fast I/O. Experimental results show that the proposed scheme reduces the deadline miss ratio of real-time applications by 92% compared to conventional blocking I/O used in Android.